1. Field of the Invention
The present invention relates to a logic circuit using a two-terminal switching device having two stable resistivity values against an applied voltage.
2. Description of Related Art
In recent years, the development of characteristics of an electronic device using an organic electronic material has been remarkable. For example, in organic EL displays or organic LED displays, since each pixel individually emits light (or more specifically, spontaneously emits light), they have a number of advantages, such as an advantage that they have a wide viewing angle that a color filter is not necessary; an advantage that a backlight is not necessary so that thinning is possible; and an advantage that they can be formed on a flexible substrate such as plastic, as compared with conventional liquid crystals.
Also, in a circuit system for driving an electronic device of this kind, the use of an organic material is studied. If this is possible, it is expected that an electronic device in which a substrate can be deformed, such as a wearable PC and a flexible display, is realized.
In addition, in RFID (radio frequency identification) technology, which has been eagerly utilized in recent years, the utilization of an organic electronic device is studied. In this RFID technology, data is stored or read out in a medium in a card form or tag form by using a radio wave, and the foregoing data is recognized by communication via an antenna. That is, the data is exchanged by radio between a small-sized medium such as a tag and a device designated as a reader.
Since RFID is convenient in that it is not necessary to bring the tag or the like into contact with the reader if they are in communication range, its application tends to spread. However, since the unit price of a current tag is several tens of yen or more, a problem arises in that it is too expensive to attach to a commodity with a low price.
At present, while IC using a silicon chip is used in a tag, for the purpose of solving the foregoing problem, the use of a tag made of an organic electronic device is studied.
As one example of the foregoing organic electronic device, a CMOS circuit that is configured to have a transistor made of an organic electronic material is proposed. This can be suitably used as a so-called “combination logic circuit” (see, for example, JP 09-199732 A, JP 2001-177109 A, JP 2001-203364 A or JP 2002-324931 A).
The foregoing organic electronic material is formed as a thin film on a substrate. This thin film made of an organic electronic material is formed so as to have a film thickness in the range of from approximately several tens to several hundreds nm by a measure such as vacuum vapor deposition and solution coating (for example, a spin coating method and an inkjet method).
Glass, silicon, and plastics are frequently used as the material of the foregoing substrate. On this substrate, a metal electrode, an electrode made of an oxide such as ITO, an insulating film, and so on are formed by employing a measure such as vacuum vapor deposition, solution coating (for example, a spin coating method and an inkjet method), sputtering, CVD, and PVD as the need arises.
In the foregoing, in particular, the use of an organic material as the electronic material brings such merits that the manufacturing costs are low; that the processing temperature is low; and that flexible electric appliances can be manufactured by using a plastic substrate.
However, a concrete proposal has not yet been made to configure a flip-flop circuit (bistable circuit), which is necessary for a “sequential logic circuit”, as opposed to a “combination logic circuit”, by using an organic electronic material device. Here, in the “combination logic circuit”, an output value is determined by a combination of input logic values at the present point in time; and in the “sequential logic circuit”, an output value is determined by a time series of input logic values to the present point in time.
Generally, when using conventional silicon devices, a sequential logic circuit made of a combination of plural transistors and rectifying devices is employed. However, in sequential logic circuits using silicon devices, preparing an organic transistor is complicated. Thus, a problem has arisen that characteristics are so widely scattered that the yield rate is low.